Soon after Moran returned east, Ferdinand Hayden and others (including executives of the Northern Pacific Railroad), began promoting the idea that Yellowstone should be protected and preserved as a national park.
Because no member of Congress had seen Yellowstone, Hayden and his colleagues brought Moran's watercolors, along with the photographs taken by William Henry Jackson on the 1871 expedition, to Capitol Hill. Their images were later
reported to have played a decisive role in the debate that led to the establishment of Yellowstone as the first national park in March 1872.